As one example of a carbon filament, a carbon nanotube (CNT) has excellent properties and is accordingly expected to be employed in a variety of industrial applications. For example, a CNT provides substantially as low an electrical resistance value as copper and is thus considered to be used as a material for wire. Furthermore, such CNT is produced in a variety of methods, as proposed for example in Japanese Patent Laying-Open No. 2007-112662 (Patent Document 1).
Japanese Patent Laying-Open No. 2007-112662 proposes a method in which a metal catalyst of gallium (Ga) is introduced in an amorphous carbon wire structure and a direct current is applied thereto to produce a CNT sized, shaped and oriented as desired.
When a carbon atom is chemically bonded by an sp2 hybridized orbital, it forms a lattice-structured film having two dimensionally spread carbocyclic six-membered rings packed in a plane. This carbon atom's two dimensional planar structure is referred to as graphene. As a special example, graphene in a tubular closed structure is a carbon nanotube, and graphene layers stacked in a direction of a normal thereto are graphite.
A carbon nanotube is a tubular material having a diameter equal to or smaller than 1 μm and ideally, a film in a lattice structure of carbocyclic six-membered rings has planes parallel to a tube's axis to form the tube, and a multiple of such tubes may be provided. The carbon nanotube is theoretically expected to exhibit a metallic property or a semiconducting property depending on how the lattice structured films have carbocyclic six-membered rings linked and the tube's thickness, and it is thus expected as a future high-performance material.
For example, Japanese Patent Laying-Open No. 2007-63051 (Patent Document 2), Japanese Patent Laying-Open No. 2002-255528 (Patent Document 3), Japanese Patent Laying-Open No. 2003-238126 (Patent Document 4), and Japanese Patent Laying-Open No. 2000-86219 (Patent Document 5) disclose organizing carbon nanotubes to provide a structure by dispersing carbon nanotubes in a dispersion medium for example ultrasonically to prepare a dispersion liquid of carbon nanotubes which is in turn dropped on a planar substrate and dried thereon to provide a thin film of carbon nanotubes. However, the thin film of carbon nanotubes has the carbon nanotubes interconnected simply by contacting one another, and is thus disadvantageously high in contact resistance.
Graphite has a variety of electrical properties, as observed on graphite film, such as a bandgap, a fractional quantum Hall effect and the like varying with in what size it is cut out, and is thus gaining a large attention in recent years not only for physical phenomena but also in terms of application to devices in the future.
K. S, Novoselov et. al., Science 306 (2004) pp. 666-669. (Non Patent Document 1), K. S, Novoselov et. al., Proc. Natl. Acad. Sci. U.S.A. 102 (2005) pp. 10451-10453. (Non Patent Document 2), C. Berger et. al., J. Phys. Chem. B108 (2004) pp. 19912-19916. (Non Patent Document 3), and Yuanbo Zhang et. al., Nature 438, pp. 201-204 (10 Nov. 2005) (Non Patent Document 4) disclose techniques used to produce a monolayer of graphite film, i.e., graphene.
Typical conventional techniques are provided by K. S, Novoselov et. al., Science 306 (2004) pp. 666-669. (Non Patent Document 1), and K. S, Novoselov et. al., Proc. Natl. Acad. Sci. U.S.A. 102 (2005) pp. 10451-10453. (Non Patent Document 2). More specifically, Scotch tape is stuck on graphite crystal to peel off graphite to leave a single sheet of graphene on a silicon substrate having a surface oxidized and a monolayer of graphene is found and utilized. This technique is a rather primitive technique.
C. Berger et. al., J. Phys. Chem. B108 (2004) pp. 19912-19916. (Non Patent Document 3) discloses that a high temperature process at 1400-1600° C. is performed in an environment of ultrahigh vacuum to decompose a SiC monocrystalline surface and after Si is selectively sublimated a monolayer of graphene is synthesized. Furthermore, it is also disclosed that a diamond microcrystal is first formed and then processed at 1600° C. to obtain graphene from diamond.
Yuanbo Zhang et. al., Nature 438, pp. 201-204 (10 Nov. 2005) (Non Patent Document 4) discloses a method employing chemical vapor deposition to produce graphene. More specifically, camphor vapor is thermally decomposed at 700-850° C. at an Ni crystal face to obtain graphene.
It is difficult, however, to use these methods to handle general, industrial production, and furthermore, the methods cannot provide a large area of graphite film essential to device application.